Endothelium-Derived Relaxing Factor
Endothelial cells have been shown to produce a potent vasodilator known as Endothelium-Derived Relaxing Factor (EDRF). Many naturally occurring substances which act as physiological vasodilators mediate all or part of their action by stimulating the release of EDRF. Examples of such substances include acetylcholine, histamine, bradykinin, leukotrienes, ADP, and ATP. Recent studies have identified EDRF as nitric oxide, a short lived, unstable compound (Ignarro et al., 1987, Proc. Natl. Acad. Sci. U.S.A. 84:9265-9269 and Palmer et al., 1987, Nature 327:524-526).
L-Arginine is the metabolic precursor of EDRF (Schmidt et al., 1988, Eur. J. Pharmacol. 154:213-216). N.sup.G -methyl-L-arginine is a competitive inhibitor of the biosynthetic pathway of EDRF (Palmer et al., 1988, Nature 333:664-666). Administration of N.sup.G -methyl-L-arginine to guinea pigs and rabbits has been shown to increase blood pressure (Aisaka et al., 1989, Biochem. Biophys. Res. Commun. 160:881-886). Nitric oxide (NO) appears to be synthesized from L-arginine by the enzyme, NO synthase; the coproduct is L-citrulline (Moncada et al., 1991, J Cardiovascular Pharmacol. 17 (Suppl. 3):S1-S9). NO is an endogenous stimulator for soluble guanylate cyclase.
Nitric oxide has been found to be produced by macrophages, endothelial cells, neutrophils, Kupffer cells and hepatocytes, murine fibroblasts stimulated with cytokines, and EMT-6 cells, a spontaneous reurine mammary adenocarcinoma cell line when treated with cytokine (reviewed in Moncada et al., 1991, Pharmacol. Reviews 43:109-142). Specifically, macrophage cells become activated by 12-36 hour treatments with gamma-interferon, bacterial endotoxin and various cytokines (reviewed in Collier and Vallance, 1989, Trends in Pharmacol. Sci. 10:427-431).
Endothelial cells in the presence of gamma-interferon, have been found to secrete large quantities of arginine-derived nitrogen oxides after activation by tumor necrosis factor (TNF) or endotoxin (Kilbourn and Belloni, 1990, J. Natl. Cancer Inst. 82:772-776). TNF causes marked hypotension in mammals (Tracey et al., 1986, Gynecol. Obstet. 164:415-422; Old, 1985, Science 230:630-632). Additionally, TNF is thought to mediate the vascular collapse resulting from bacterial endotoxin (Beutler et al., 1985, Science 229:869-871). It has recently been shown that arginine derivatives inhibit systemic hypotension associated with nitric oxide production, specifically treatment with TNF, gamma interferon, interleukin-2, and bacterial endotoxin (Kilbourn et al., U.S. Pat. No. 5,028,627, issued Jul. 2, 1991; PCT lypplication no. WO 91/04023, published Apr. 4, 1991; and Kilbourn et al., 1990, Proc. Natl. Acad. Sci. U.S.A. 87:3629-3632). Nitric oxide overproduction is also thought to be involved in numerous other pathogenic or potentially pathogenic syndromes. For example, some of these syndromes are thought to be associated with malaria, senescence and diabetes. The procedures of the present invention may also be used to prevent, inhibit and/or alleviate such NO-related syndromes.